Conventionally, a sensor, which is mounted to an intake system (e.g., an intake pipe or an intake manifold) or an exhaust system of an internal combustion engine such as a diesel engine or a gasoline engine, has been known and is used for detecting the concentration of a specific gas component (e.g., oxygen or NOx) in a measurement target gas (e.g., Japanese Laid-Open Patent Publication No. 2007-71582). This sensor includes: a plate-shaped detection element extending in an axial direction and having an electrode terminal portion (electrical connection terminal portion) formed on a rear side of the detection element in the axial direction; a metal terminal member (connection terminal) electrically connected to the electrode terminal portion to form a current path; and a separator into which the metal terminal member is inserted (e.g., Japanese Laid-Open Patent Publication No. 2007-71582).
The metal terminal member disclosed in Japanese Laid-Open Patent Publication No. 2007-71582 includes: an elongated frame body portion extending in the axial direction; and an element contact portion that is folded back from a front end portion of the frame body portion to the rear side in the axial direction, and is in contact with the electrode terminal portion. The metal terminal member has an engagement portion for positioning itself with respect to the separator. The engagement portion protrudes from the frame body portion toward a side opposite to the side where the detection element is located, and is engaged with the separator to regulate movement of the frame body portion.